The present invention concerns an electronic watch with a display by means of discs.
It is well known that, in analog watches, the display may be of two main kinds: either by means of hands or pointers which are driven by spindles, or by means of discs which are driven in rotation and which carry marks simulating the hands or pointers. Thus there is for example an hours disc and a minutes disc.
The present invention is concerned solely with the second kind of analog display.
A number of designs have already been proposed, in regard to guiding and driving the discs in rotation. In accordance with Swiss Pat. No. 307,045 which describes a mechanical watch, the hours disc is directly carried and driven by the spring drum cover. The minutes discs are provided with a peripheral tooth arrangement and a gear train engaged with the tooth arrangements of the discs transmits the movement of the hours disc to the minutes disc, in a suitable ratio. This construction is relatively bulky because of the stacked arrangement of the drive member formed by the spring drum and the two discs. In addition, because the two discs are of substantially the same diameter, it is the gear train alone which is required to provide the multiplication ratio. Consequently, the gear train must comprise at least three movement means which are disposed outside the discs. The number of movement means increases the complexity of machining of the bridge members which carry them, and increases the dimensions of the watch. In accordance with Swiss Pat. No. 155,524, the two discs are free to rotate about a spindle and are provided with a tooth arrangement at their respective peripheries. Each disc is driven by a train of movement members, which is disposed outside the discs and which engages with the tooth arrangement. The two trains of movement members are therefore mounted in parallel and are driven by a single drive member.
This design therefore requires a substantial number of movement members. This increases the complexity of the watch and also increases the number of apertures to be made in the bridge members or plates which carry the movement members. In addition, the trains of movement members take up a relatively substantial amount of space.
It will be seen that the two prior art constructions do not represent the optimum design if the watch comprising such discs is required to be as thin as possible. The present-day tendency is towards watches which are as small in thickness as possible, being referred to as "extra-thin" watches.